KIN 292 1st Edition Lecture 9 These are the notes from Professor Starnes lecture of Clinical Human Physiology These come from the slideshows provided by the professor and include extra notes and explanations Highlighted or bolded information are things that I believe to be information that is important to look over multiple times The notes in red are my personal additions and quotes of Professor Starnes from the class lecture Chapter 4 Cell Membrane Transport Outline of Last Lecture I 4 1 Factors Affecting the Direction of Transport II 4 2 Rate of Transport III 4 3 Passive Transport Outline of Current Lecture I 4 5 Osmosis Passive Transport of Current Lecture Recap Membranes Are Selective Selectively permeable Permeable allow molecules to pass through Selective restrictive Membranes allow the transport of some substances but not others Coordinated movement of substances across membranes or preventing movement as the case may be is crucial for physiological function of all cells and organs Nonpolar molecules o Easily transported across membrane o Examples O2 CO2 fatty acids o Soluble and permeable in fats Ions and polar molecules o Normally not transported o Need help to cross nonpolar lipid bilayer o Examples Glucose proteins Na These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Factors Affecting the Direction of Transport Passive vs Active think exergonic and endogonic reactions Passive Transport o Spontaneous Driving force is to decrease difference between sides Like the mechanical box Potential energy comes from difference between sides for concentration electrical charge or both o Active Transport o Not spontaneous moves to increase difference o Requires input of energy Examples ATP NADH for electron transport chain to pump H across inner mitochondrial membrane Figure 4 1 Chemical driving forces Concentration difference or gradient C provides potential energy that can push particles from higher to lower concentration areas o o Lipid bilayer is freely permeable to non polar molecules o Simple diffusion movement depends only on concentration o Polar molecules are not freely permeable and require C and specialized proteins embedded in the membrane to get through described later Electrical Driving Force Membrane potential Vm o Is a force Caused by unequal distribution of anions negatively charged ion and cations positively charged ion across the cell membrane o Magnitude of driving force depends on magnitude of charge separation source of energy Principles o Opposite charges attract and Like charges repel Figure 4 2 Electrical driving force caused by unequal distribution of anions negatively charged ion and cations positively charged ion across the cell membrane Note that excess charges on either side tend to cluster near the membrane Simple Principle Opposite charges attract and Like charges repel Figure 4 4 Magnitude of electrical driving force is determined by Membrane Potential Vm and valence voltageacross the membrane is only half as much Valence The number of electrons in an atom s outermost shell Determines amount of charge on the particle and governs bonding behavior Chem Review p 22 Electrochemical Driving Force Vm is the magnitude of the charge difference between inside ICF and outside ECF of cell Measured in millivolts Has a polarity reference is ICF Note that the driving force for the divalent cation in c is the same as for the monovalent cation in b although the Total force acting on particles Sum of chemical and electrical forces If chemical and electrical forces act in the same direction o Electrochemical force acts in the direction of each force o Magnitude sum of the chemical force and the electrical force o Example mitochondria s electrochemical gradient also called its membrane potential If chemical and electrical forces act in opposite directions o Electrochemical force acts in the direction of the stronger force o Magnitude larger force minus smaller force Question If a chemical gradient existed under which conditions would a particle not be transported across a membrane even if it is permeable to that particle Answer When the electrical force is equal to but opposite in direction to the chemical force Equilibrium Potential Ex where x represents chemical symbol for a specific ion Potassium K shown below The value for the Membrane potential Vm when Electrical force is equal and opposite to the chemical force resulting in an electrochemical force of zero EK Vm and No net movement of the ion potassium At equilibrium concentration in intracellular and extracellular is not equal Equilibrium potential is set and never changes Membrane potential changes What happens when Vm is not equal to Ex If Vm Ex E force and EC force is in direction of C force which is the force with the greatest magnitude panel b If Vm Ex E force and EC force is in direction of E force What happens when Vm is not equal to Ex In simple passive diffusion situations ions move in the direction of the EC force to attempt to return to Ex In Vm Ex left K moves outward to attempt to restore E force Does this sound similar to nearequilibrium enzymes Ex compared to Equilibrium Constant K In simple passive diffusion situations ions move in the direction of the electrochemical force force to attempt to return to Ex For reactions catalyzed by near equilibrium enzymes molecules move in the direction of the equilibrium constant mass action to attempt to return to K Toolbox Eqilibrium Potential and the Nernst Equation E I 61mV Io Log Z Ii Computation of El Nernst equation where El equilibrium potential of ion l Note book switches from Ex to El Z valence of ion l I o ECF concentration of ion l at steady state I i ICF concentration of ion l at steady state Toolbox Equilibrium Potential and the Nernst Equation Types of Passive Transport Simple diffusion No membrane proteins are needed Transport is through the bilipid layer Facilitated diffusion through a carrier which is a transmembrane protein with binding sites for specific molecules or ions Changes shape conformation as particle moves through Diffusion through channels which are transmembrane proteins that form pores passage ways specific to a particle Simple Diffusion and Fick s Law Factors affecting the rate Flux rate Magnitude of the driving force conc diff C Fig 4 7 is just like mechanical box Rate slows over time as concentration difference decreases